Abstract The majority of validated social-communication measures for children with autism spectrum disorder (ASD) were designed to behaviorally phenotype or diagnose this core symptom domain and not to detect change over time. The lack of validated outcome measures has somewhat stifled intervention research efforts as well as early interventionists? ability to monitor the effects of their programs on children?s social-communicative outcomes. It has become difficult to sort out whether non-significant treatment effects are a result of truly ineffective interventions, or rather poorly validated measures for this population. We know that the early, foundational social-communication and language skills of children with ASD predict their functioning into adolescence and even adulthood, with functional use of language by age 5 being one of the best predictors of long-term prognosis. As such, clinicians have begun to focus their efforts on improving children?s social- communication and language skills using both developmental and behavioral interventions as well as pharmaceutical treatments. In reviewing these treatment trials, it is clear there is a range of intervention success and even more clear that we lack a consistent set of outcome measures for the social-communication symptom domain. Our group has been working to validate measures of key social-communication and language skills and are able to draw from a wealth of prior psychometric data to adapt and validate a brief observational measure that can be easily used within clinical trials as well as within routine care and practice. We propose to adapt and psychometrically validate a measure of social-communication and language skills for young children, ages 12 ? 60 months, preliminarily or formally diagnosed with ASD. Specifically, we plan to validate the Early Communication Indicator for Autism Spectrum Disorder (ECI-ASD) using a robust and representative multisite sample of well-characterized children with ASD (n = 400). The current version of the ECI is norm-referenced and allows for progress monitoring, which means the measure can be used in a formative, data-driven fashion to monitor children?s intervention progress and make changes if children are not improving, but it also can provide summative outcome data. In addition, the current measure can be scored live using a mobile app. Currently, no other current social-communication measure specifically designed for children with ASD easily allows for ongoing intervention progress monitoring, data visualization, and live scoring, which will make the adapted ECI-ASD a unique outcome measurement tool. Further, the ECI-ASD will provide the ability to enter data into an online platform to compare the progress of children with ASD to normative data and this represents a sorely needed and clear innovation above current measurement approaches. The expected deliverable is a novel outcome measure of key social-communication and language skills that is psychometrically sound, minimally burdensome to administer and score, and sensitive to the incremental change expected for young children with ASD.